Incorporating Stable Water Isotopes in the Community Land Model Xinping Zhang 1 Guoyue Niu 2 Zongliang Yang 2 1 College of Resources and Environmental Sciences Hunan Normal University, Changsha, China 2 Department of Geological Sciences, the University of Texas at Austin, Texas, USA

1. Introduction

☞ Determination of the atmospheric circulation patterns and global or local water cycle mechanisms ☞ Recovery of paleoclimatic records in mid-high latitudes: the index as temperature in monsoon regions: the index as strength of monsoon or precipitation amount ☞ Investigations for water or vapor resources inventory The main objective conducting the global survey program:

iPILPS is a new type of PILPS experiment in which the process of international intercomparison will inform, illuminate and educate the land-surface scheme (LSS) parameterization community while new aspects of LSS are being developed. iPILPS: Isotops in Project for Intercomparison of Land-surface Parameterization Schemes (PILPS)

The iPILPS Phase 1 experiment aims to 1. identify and test ILSSs (isotopically enabled land-surface schemes) which incorporate SWIs (stable water isotope) 2. appraise SWI data applicable to hydro-climatic and water resource aspects of ILSSs; 3. identify observational data gaps required for evaluating ILSSs; 4. apply SWI data to specific predictions of well-understood locations simulated by available ILSSs.

In the study, stable water isotopes are added to the Community Land Model (CLM) as a diagnostic tool for an in-depth understanding of the hydrologic and thermal processes; and the diurnally and monthly variations of stable water isotopes in different reservoirs at Manaus, Brazil, are simulated and intercompared in a given year, using the CLM.

Baisic equations On the monthly time scale: water mass balance: Pr j － Evap j － Ro j － ΔS j =0 isotope mass balance: δPr j ×Pr j － δEvap j ×Evap j － δRo j ×Ro j － δΔS j ×ΔS j =0 δPr j monthly isotopic δ value of precipitation Pr j δEvap j monthly isotopic δ value of evaporation Evap j δRo j monthly isotopic δ value of surface plus subsurface runoff Ro j δΔS j monthly isotopic δ value of the change in the total storage water Evap j

R l : stable isotopic ratio in water; f: residual proportion of evaporating water body α: α=R l /R v （＞ 1) stable isotopic fractionation factor between liquid and vapor. α = α(T) on the equilibrium fractionation α = α k (T, h, V, D) on the kinetic fractionation Basic fractionation equations 1. Rayleigh evaporation fractionation equation:

2. Rayleigh condensation fractionation equation: R v : stable isotopic ratio in vapor; f: residual proportion of condensing vapor

3.1 Seasonal variations of daily- averaged  18 O and precipitation 3. Results

The seasonal variations of daily precipitation and daily-averaged  18 O in vapor and in precipitation at Manaus, Brazil

The seasonal variations of daily canopy dew, canopy reservoir and canopy evaporation, and their daily-averaged  18 O at Manaus, Brazil

The seasonal variations of daily surface dew and surface runoff, and their daily-averaged  18 O at Manaus, Brazil

3.2 Simulation of monthly-averaged  18 O and waters (moisture)

The seasonal variations of monthly canopy dew, canopy reservoir and canopy evaporation, and their monthly-averaged  18 O at Manaus, Brazil

Comparisons between actual survey and simulation on month time scale at Manaus

3.3 Simulation of monthly-averaged  18 O and waters (moisture)

The diurnal variation of  18 O in canopy dew, canopy reservoir and canopy evaporation for January (a) and July (b) at Manaus (a) time (hours) (b)

The diurnal variation of  18 O in surface dew and surface runoff for January (a) and July (b) at Manaus (a) time (hours) (b)

3.4 Simulation of Meteoric Water Line (MWL)

simulated Comparisons between actual and simulated MWLs in precipitation

Simulated MWL in surface runoff

3.5 Sensitivity test scheme 1: fpi = 1. - exp(-0.5*(clm%elai + clm%esai)) scheme 2: fpi = min(0.1,1. - exp(-0.5*(clm%elai + clm%esai))) scheme 3: fpi = min(0.2,1. - exp(-0.5*(clm%elai + clm%esai)))

Variations of  18 O in surface soil reservoir for different scheme

Variations of  18 O in sub-surface soil reservoir for different schemes

Variations of  18 O in transpiration for different schemes

4. conclusions 1. Simulations show reasonable features in the seasonal and diurnal variations of δ 18 O in canopy and surface reservoirs; 2. Owing to originating mainly from atmospheric precipitation, the stable water isotopes in these reservoirs change as the stable isotopes in precipitation; 3. On the diurnally time scale, the stable isotopes in precipitation display the typical isotopic signature in evergreen tropical forest: the heavy rains are usually depleted in stable isotopes, but the light ones are usually enriched; 4. On the monthly time scale, δ 18 O in reservoirs have distinct seasonal variation with two peaks. The feature called as amount effect is consistent with the actual survey at Manaus, from 1965 to 1990, set up by IAEA/WMO; 5. Different hydrological process cause very different isotopic responses.

End of Presentation